Redox Mediator-Coated Air-Electrodes for High-Capacity Cycle Operation of Lithium-Air Batteries

Lithium-air batteries (LAB) provide high energy density storage as high as 3,500 Wh/kg, but the poor discharge- charge cycle performance hinders their practical application. In this study, lithium bromide (LiBr) was used as a redox mediator (RM) and coated on carbon nanotube (CNT) sheets to fabricate air-electrodes for LABs with enhanced cycle performance at a high capacity (4 mAh/cm2), twice the capacity of the current lithium-ion battery technology. The CNT-based electrodes attained a 3 -fold longer cycle life than that of the conventional Ketjen Black cathodes. The LiBr-loaded CNT cathode suppressed overpotential in discharging and charging, in contrast to cells with LiBr incorporated in the electrolyte. The X-ray diffraction analysis revealed that the LiBr-loaded air-electrode decreased the crystallinity of the discharge product, Li2O2, plated during discharge, which resulted in the suppression of the cathode resistance. The rotating ring-disk electrode displayed an enhanced surface reduction pathway for the oxygen reduction reaction in the LiBr-loaded cathode, which lowered the Li2O2 crystallinity. This demonstrates the potential of the LiBr-coated CNT cathode for improving the overall cycle performance of LABs.